Delayed cerebral ischemia (DCI) following subarachnoid hemorrhage (SAH) remains a significant cause of brain injury and disability. Cerebral vasospasm remains a treatable cause of DCI. Mitigation of brain ischemia from cerebral vasospasm is possible by increasing arterial blood pressure, infusing, vasodilators, and performing cerebral angioplasty. If cerebral vasospasm is detected prior to the development of cerebral ischemia, morbidity can be reduced, or eliminated. Therefore, the reduction in morbidity is dependent on the accurate and early detection of cerebral vasospasm.
The detection of cerebral vasospasm is currently problematic. Although cerebral vasospasm may be suspected by change in clinical status alone—namely, decrease in level of consciousness or new focal neurological deficit—these changes may be non-specific resulting in high false positive rate for predicting true cerebral vasospasm. Transcranial Doppler (TCD), CT angiography and CT perfusion, and MR perfusion have ability to document vessel caliber change either directly or indirectly, but each technique is not ideal. For imaging-based techniques (CT and MRI) both contrast administration and the necessary transport of the patient make such recordings challenging and only provide episodic measure of vascular status. TCD—although a portable technique—is operator dependent and is unable to interrogate vessels beyond the Circle of Willis. The creation of a non-invasive, portable method that samples more vascular territory is needed.